Acoustic device



Sept. 21, 1937.

A. E. SWICKARD ACOUSTIC DEVICE Filed July 30, 1956 FIG. 2

L DNDENSER TRANSM/ T TER RIB BON TRANSM/ TTE'R 7W5 TOR A. 5. sw/c/rARo MW 6. 7M

ATTORNEY 2 5 'fsupport.

Patented Sept. 21, 1937 UNITED STAT S v 2,093,664 AcoUs'rIc DEVICE Andrew E. Swickard, East Orange, N.'J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July so, 1936, Serial No. 93,355

7 Claim.

This invention relates to acoustic devices and, more particularly to a combination of transmitters.

. An object of this invention is to translate sound .5 waves'with efliciency and fidelity over a desired frequency range.

'Afeatureof the invention comprises the coin-.

awelocity-type transmitter and a pressure-type transmitter, the electrical outputs ofthe transmitters working. into a single amplifier only. Still another feature comprises such a com- I bination ina circuit containing means for circa-- tively eliminating one orthe other transmitter as a sound translating device in the combination. A f;urther feature comprises a ribbon typefvelocity transmitter and a condenser type pressure trans itter in v close proximity on a common o Qtherandifurther featuresfwillbe apparent {from the descriptive matter that follows hereinafter. l

A more completeunderstanding of the inven- .tionfwill beobtained from the'followihg detailed esc iion ken m'f fe iunc onl fi he" ppended drawing wherein: i M if Fig. 1 is a perspective view o ansmitte'r combination. 7 or acoustic device in "attendance with this invention, partly broken away; and

Fig. 2 is a schematic of the device of Fig. 1 and its associated circuit.

With reference initially to Fig. 2, there is disclosed a circuit or system comprising a transmitter I0, preferably of the type having a'vibratile element or diaphragm adapted to respond to the velocity component of incident sound waves, and preferably of the conductive ribbon diaphragm type, and asecond transmitter H, preferably of the type having a vibratile element or diaphragm adaptedto respond to the pressure component of the sound waves, and preferably of the electrostatic or condenser type. The output terminals of the transmitter 10 are connected to the ends of the primary winding I2 of transformer III, the secondary winding ll of which is connected in series with transmitter II. A circuit controller or switch I5 is connected in shunt with thewinding I, being normally open with the blade l6 ofl the contact II. The condenser clamping member 32 and. screws 33." Th

.ductive ribbon diaphragm 31 is suppp transmitter is charged from a. suitable source of constant potential, such as the battery It, a resistor IQ of large resistance, for example, of the order of 50 to megohms, being connected in series with the battery, A circuit controller 5 or switch 20 is provided-in series with the batteryso that when the'blade 2| is off the contact .22, polarizing voltage is removed from the con denser transmitter. The condenser '23, blocks the battery potential from thecont'rol electrode 10 or grid 24 of an amplifier 25, for example, athreeelectrode electron discharge device; Resistor 25 is agrid leak resistanceofthe order of 5 0to 100 megohms.

The transmitter l llv comprises a 'UQ r. 5

shoeshapedpermanent magnet 30], tart: pole-pieces 3| being secured to its; ends bye pieces definea'magnetic' airgap in whi ends of the ribbcn being secured between; lating clamping plates 35. The transmit}; v is ofminiature size and restsf onjthe' or v Q36 of,jan,, H shaped,.support. 31, the upri .and cross-bar of which are secured togetlie an i 25 t the. magnetibyabolt.,39. nd'screwjau. The H qqm-mon siipport 4| for 'theijtransmittersjj coal";-

s l ffi d j -co in flzghavm i en: la'r'sed. .hbuow; ndi' b'l iq or fc s .,p 3. sache s the transformer [3,the amplifier 25','theresistors' 30 1,9, 2 6, and thesrcondenser 23, and supporting the t ti ss l 5. .2 ,A.,.r, u t, ;p tut ext nsion, o ,the'baseijprovideslal protective en e fqr the H ffli"ele a -J animus of sf pressu e r n 35 mitter such" as '"l I, and a velocity transmitter such as H], are properly combined, a unidirectional transmitter. is obtained. The velocity transmitter discriminates against sound waves coming from the sides, but not from the back or 40 the front of its diaphragm. The pressure device picks up sound waves from all directions without discrimination. When their electrical outputs are combined it is found that a unidirectional characteristic is obtained, since the electrical out- 45 put of the velocity device is out of phase with that of the pressure device for sound coming from the rear.

Generally, the voltage generated by the transmitter combination should be in phase with the 50 open sound field pressure throughout the entire frequency range. This phase requirement mitigates against the use of transmitters with involved acoustic circuits associated with the diaphragm, since such circuits tend to produce 55 phase distortion. Since a ribbon velocity transmitter is mass-controlled throughout its entire working frequency range, its electrical output is in phase with the sound field pressure; this is.

ideal for the velocity transmitter for the unidirectional combination. The voltage generated by a condenser transmitter is in phase with the sound field pressure throughout the frequency range where the mechanical impedance of its diaphragm is substantially that of a stiffness. If the diaphragm resonanceis made to occur at a sufilciently high frequency a satisfactory pressure device is obtained for the unidirectional combination. The condenser transmitter, furthermore, should be sufiiciently small so that the efiects of diffraction therearound are not appreciable in the frequency range over which it is desired that the unidirectional combination be effective.

With the ribbon and the condenser transmitter combination, the terminals of the ribbon transmitter transformer secondary winding are connected between the low impedance terminal 01' the condenser transmitter and the ground lead of the associated amplifier. The combination operates most satisfactorily when a single amplifier only is used for both transmitters, since the difference in phase shift between two amplifiers, if used, seriously reduces the unidirectional effect of the combination. By associating switching means with the two transmitters, it is possible to utilize one or the other separately as well as the two together. The combination, therefore, may constitute a universal transmitter in that it may serve as a pressure, a velocity or a pressure-velocity device.

Although this invention has been disclosed with reference to a specific embodiment, it will be understood that it is not restricted thereto, but is limited in scope by the appended claims only.

What is claimed is:

1. In combination, a velocity-type transmitter comprising a permanent magnet, pole-pieces supported on said magnet and defining an elongated air-gap, and a conductive ribbon diaphragm in said air-gap, a carrier member secured to said magnet, a condenser transmitter on said carrier member, and a common support for said transmitters.

2. In combination, a velocity-type transmitter comprising a U-shaped permanent magnet, polepieces supported on the ends of said magnet and defining an elongated air-gap, and a conductive ribbon diaphragm in said air-gap, a carrier member secured to said magnet, a condenser transmitter on said carrier member at one end of said diaphragm and between the arms of the magnet, and a common support for said transmitters.

3. In combination, a velocity-type transmitter, a pressure-type transmitter, and means for combining the electrical outputs of said transmitters, said means including a transformer having a primary and a secondary winding, said velocity transmitter being connected to said primary winding and said pressure transmitter being connected in series with said secondary winding.

4. In combination, a velocity-type transmitter, a pressure-type transmitter, and means for combining the electrical outputs of said transmitters, said means including a transformer having a primary and a secondary winding, said velocity transmitter being connected to said primary winding and said pressure transmitter being connected in series with said secondary winding, and a single amplifier for said transmitters.

5. In combination, a velocity-type transmitter, a pressure-type transmitter, and means for combining the electrical outputs of said transmitters, said means including a transformer having a primary and a secondary winding, said velocity transmitter being connected to said primary winding and said pressure transmitter being connected in series with said secondary winding, and switching means for cutting out at will either transmitter.

6. In combinatioma ribbon-type velocity transbining the electrical outputs of said transmitters,

said means including a transformer having a primary and a secondary winding, said velocity transmitter being connected to said primary winding and said pressure transmitter being connected in series with said secondary winding, and switching means for cutting out at will either transmitter, one switching means being connected in shunt with the secondary winding of the transformer.

ANDREW E. SW'ICKARD. 

